Newer bloggers can use the ‘upgrade automatically’ link in their dashboards to upgrade WordPress, but what happens when you have an older site with a version of WordPress that doesn’t allow for automatic upgrade?
To upgrade WordPress from older versions, deactivate all your plugins and revert to the default theme.
Download and extract all the stable versions of WordPress that have been released since your site’s current version. You can find these in the WordPress Release Archives.
Next, FTP the versions, one at a time, testing between each one. Be sure you are logged into the WordPress Admin Dashboard, and hit refresh after each new version has been uploaded. Some versions require a Database Update which you’ll be able to do with the push of a button, but you have to refresh to see it. Once you know the new version is stable, go back to the FTP client and continue. Repeat these steps till you have the latest version working on your site.
Note: I always upload all the WordPress files and folders EXCEPT wp-content. I open this and transfer the index.php file separately, and on the later versions I do the same for the index.php files in the themes and plugins folders. The reason for this is the plugins and themes included in these directories may be different versions than you have on your site and you could experience problems overwriting them.
When you’re done upgrading WordPress from an older version be sure to edit your wp-config file to secure your WordPress blog.
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